The above construction machines are driven by an operator, while the operator is walking. The machines have a possibility of running away, in case the operator tumbles over and cannot control it any more or in case he turns on the starter with the control lever keeping at the forward or backward position.
To solve the above problem, a conventional machine has been equipped with the safety device as shown in FIG. 5. The safety device comprises a control box 20, a control lever 30, a safety rod 40, and a safety arm 50. The control lever 30 is swingably supported by an axis in the control box 20. The safety rod 40 is slidably supported on the rear wall of the control box 20 and extends from the outside through the inside of the rear wall. The safety rod 40 interposes a stressed coil spring 41 in the housing 42. The upper portion of the control lever 30 is adjacent to the end of the safety rod 40 inside the control box 20 when the lever 30 is shifted to the backward position as indicated by dashed line. The safety arm 50 has a V-like shape and is pivotally supported at the corner of the V-like shape by an axis in the lower portion of the control box 20 adjacent to the front wall of the control box 20. The upper portion of the safety arm 50 inwardly extends in the control box 20. The lower end of the control lever 30 is adjacent to the upper portion of the safety arm 50 when the lever 30 is shifted to the backward position as indicated by dashed line. The lower portion of the safety arm 50 extends from the bottom to the outside of the control box 20. In case the operator is sandwiched between an obstacle and the machine moving backwardly, pushing the safety rod 40 changes the position of the control lever 30 to the neutral or forward position and then keeps the operator safe. In case the operator tumbles over and cannot operate the control lever, pushing the safety arm 30 changes the position of the control lever 30 to the neutral or forward position and then keeps the operator safe.
However the above-mentioned conventional safety device requires the operator to immediately touch another portion than the control lever 30, that is, the safety rod 40 or the safety arm 50, in order to prevent the machine from running away. If the operator unfortunately has no chance to touch such portions, it is impossible to stop the machine running away. Moreover, the safety rod 40 and the safety arm 50 are encumbrances for ordinary operations, since they extend out of the control box 20. And such structure is complicated and large, and makes the manufacturing cost expensive.
U.S. Pat. No. 4,267,804 issued to Rypka discloses a safety system which prevents a construction machine from being turned on unless the control lever is in a neutral position, thereby making the operator reminded to place the control lever in the neutral position before attempting to start the machines. Rypka provides a solution to prevent accidents which occur when the machine is started, but does not give the solution to prevent accidents which occur while the machine is in operation, e.g. when the operator in operation tumbles over.